Lamp system with green-blue gas-discharge lamp and yellow-red led

ABSTRACT

The invention relates to a lamp system having—a gas-discharge lamp with a color point in the green-blue,—an LED with a color point in the yellow-red, and—an optical component for additive mixing of the light from the gas-discharge lamp and the LED, and to a corresponding method of illumination. A blue and green emitting fluorescent lamp is particularly suitable as gas-discharge lamp, and a red-yellow-emitting AlGaInP LED or a red-emitting AlGaAs LED as LED. Through additive mixing of the light from these high-efficiency light sources, the invention provides a highly efficient light source affording good color rendering, which contains all three primary colors and is particularly suited to the highly efficient generation of white light.

The invention relates to the field of lighting, for example lighting foroffices and homes or for the illumination of sales displays. In practicea number of known light sources are used for this purpose, such asfilament lamps, halogen lamps, low-pressure and high-pressure gasdischarge lamps and of late also light-emitting diodes (LEDs).

By means of such light sources and sometimes by mixing multipleindividual sources it is possible to produce lamp systems of widelyvarying light colorations, light outputs and color renditions. However,the said light sources have widely differing efficiencies in convertingthe electrical energy used to supply the source into the light outputproduced. These efficiencies are usually between 10 lm/W for a filamentlamp and 120 lm/W for a fluorescent-lamp, that is in this case alow-pressure mercury vapor lamp, the primarily generated mercuryradiation of which is converted into visible light by suitablyfluorescent phosphors. At the same time, although there are yet moreefficient light sources, such as the SOX lamps still sometimes used forstreet lighting, some with an output of more than 200 lm/W, for example,these light sources are not white and do not possess good colorrendition. An SOX lamp, for example, essentially only emits the yellowsodium line.

In addition to the suitable choice of light coloration, light output andcolor rendition combined with high efficiency, variable-color lampsystems have recently been proposed, which allow a user, at least tosome extent, to control in particular the light coloration of the lampsystems. Thus DE 200 07 134 U1 proposes a lamp system having a whitefluorescent lamp, for example, together with one or more colored LEDs,the light from which is additively mixed by suitable means of deflectionand/or diffusion into a full homogeneous light. By varying the output ofthe colored LEDs, a user can to some extent influence their light outputand hence also the color point of the overall lamp system. U.S.2001/0005319 A1 uses red, green and blue LEDs, for example, to producewhite or colored light in one lamp system and discloses an easy-to-usecontrol device by means of which a user can control the light colorationof the lamp system within wide limits.

An object of the present invention is now to develop this prior art soas to provide a high-efficiency lamp system which simultaneously affordsgood color rendition and in particular a high-efficiency white lampsystem.

This object is achieved, on the one hand, by a lamp system having

-   -   a gas-discharge lamp with a color point in the green-blue,    -   an LED with a color point in the yellow-red, and    -   an optical component for additive mixing of the light from the        gas-discharge lamp and the LED,    -   and on the other by a method of illumination comprising the        following stages:        -   generation of light with a color point in the green-blue by            means of a gas-discharge lamp,        -   generation of light with a color point in the yellow-red by            means of an LED, and        -   additive mixing of the light from the gas-discharge lamp and            the LED by means of an optical component.

The principle of the invention is therefore based on the finding thatgas-discharge lamps possess high efficiencies in the green-blue and LEDspossess high efficiencies in the yellow-red and that through additivemixing of these two types of light sources it is possible to obtain ahigh-efficiency lamp system which simultaneously affords good colorrendition and in particular a high-efficiency white lamp system. Inparticular, through the use of a green-blue gas-discharge lamp insteadof a white fluorescent lamp, a significantly higher efficiency isobtained than in the prior art disclosed in DE 200 07 134 U1.

The dependent claims demonstrate particularly advantageous developmentsof the invention.

A fluorescent lamp, such as a low-pressure mercury vapor lamp, forexample, may be used as gas-discharge lamp. In such low-pressure mercuryvapor lamps the electrical energy is first (partially) converted intoultraviolet mercury radiation, in the 254 nm line, for example. Thisultraviolet radiation can then be converted by the blue phosphor BAM(emission around 450 nm) and the green phosphor CAT (emission around 542nm) into visible green-blue radiation.

For one embodiment of the invention, however, other gas-discharge lampsare in principle feasible. For example, many high-pressure gas dischargelamps also possess high efficiencies in the green-blue and are thereforesuitable for a lamp system according to the invention. Alternativeradiating substances to mercury have also recently been discovered,which despite their as yet low efficiencies show highly promisingpotential by virtue of their inherently lower Stokes shifts. Referencewill be made here to the molecular radiation sources disclosed by EP 1187 174 A2 and the unpublished DE 101 29 464.6 as representativeexamples of these substances.

Possible LEDs, for example, are an inorganic red-yellow emitting AlGaInPLED (emission in the range 600-620 nm) or an inorganic red emittingAlGaAs LED. Since these LEDs possess higher efficiencies thangas-discharge lamps in converting the electrical energy into red-yellowor red radiation, through additive mixing of the green-blue with thered-yellow light sources in accordance with the invention, ahigh-efficiency light source is obtained with good color rendition. Thisapproach leads, in particular, to a lamp system with white lightcoloration having an efficiency which exceeds the aforementioned peakvalue of 120 lm/W for hitherto known white light sources giving goodcolor rendition. In addition to these types of LED just mentioned,however, consideration may naturally also be given to all other typeshaving sufficiently high efficiencies in the yellow-red.

It is possible to determine the light coloration of a lamp systemaccording to the invention by varying the light outputs of theindividual light sources involved in the mixing. To do this, theelectrical input of the gas-discharge lamp and/or the LEDs can firstlybe varied, the LEDs being particularly easy to trigger. Secondly, as anaddition or as an alternative to this, controllable mixing componentsare also feasible, such as switchable filters or moveable diaphragms,reflectors, lenses, diffusion elements or the like. As alreadymentioned, a method of controlling the light coloration of the overalllamp system easily operated by the end user is disclosed by U.S.2001/0005319 A1, to which end this specification will hereby beincorporated in its entirety into the present application. Variouspossible ways of arranging the light sources in a housing and the choiceof mixing components are, as stated above, disclosed by DE 200 07 134U1, which to this end will hereby also be incorporated into theapplication.

The invention will be further described with reference to examples ofembodiments shown in the drawings to which, however, the invention isnot restricted. In the drawings:

FIG. 1 shows a sectional view through a lamp system according to theinvention, and

FIG. 2 shows a plan view from below of the lamp system in FIG. 1.

A fluorescent lamp, in particular a low-pressure mercury vapor lamp maybe selected as gas-discharge lamp. As already stated, in the case ofsuch low-pressure mercury vapor lamps the electrical energy is first(partially) converted into the ultraviolet mercury radiation of the 254nm-line. This efficiency of this conversion is approximately 60%. Withregard to the efficiency of the BAM and CAT phosphors for the conversionof UV light into visible light, allowance must first be made for thefact that the conversion of a UV quantum at 254 nm into a visible blue(at 450 nm) or a visible green (at 542 nm) leads to the energydifference between these quanta (between 254 and 450 or between 254 and542 nm) being lost in the form of the so-called Stokes shift(single-quantum phosphors). In addition to this there may be otherquantum loss mechanisms, although these are of lesser significance. Theso-called physical efficiency of the conversion of electrical energyinto visible radiation in such a lamp is therefore about 28% for green(at approximately 542 nm) and 34% for blue (at approximately 450 nm).

Taking further account of the different ocular sensitivities V(λ) atdifferent wavelengths λ, the physical efficiencies are multiplied by“V(λ)*683 lm/W” in order to obtain the lighting efficiencies. TakingV(542 nm) as =0.98, the latter amount to 185 lm/W in the green andtaking V(450 nm) as =0.044 they amount to 10 lm/W in the blue.

In addition to the green and the blue phosphor, a typical warm whitefluorescent lamp (color: 83, Ra value: 80, color temperature: 3000K)also uses a red phosphor, such as YOX (emission around 610 nm) and theelectrical energy is divided up into red:green:blue in the ratio55:40:5. Owing to the large Stokes shift in the red, the physicalefficiency there, however, is only 25%, giving a lighting efficiency,where V(610 nm)=0.5, of 85 lm/W. The overall efficiency of such a lampis therefore only (0.55*85+0.4*185+0.05*10)lm/W=120 lm/W, whichcorresponds to the efficiency initially quoted.

The efficiency of the overall lamp system can therefore be increased ifa more efficient LED is used in place of the red phosphor (around 610nm) with a lighting efficiency of 85 lm/W. The yellow-red AlGaInP LEDsnow available, which emit in the range between 600-620 nm, alreadyafford efficiencies in excess of 100 lm/W, which already makes themsuperior to the 85 lm/W of the red phosphor, thereby leading to moreefficient overall lamp systems. Experts predict that in the near futurethese LEDs will attain efficiencies of up to 150 lm/W, so that theefficiency in the red would increase by a factor of 150/85=1.76. Forsuch LEDs the resulting efficiency of the overall lamp system would be(0.55*150+0.4*185+0.05*10)lm/W=157 lm/W, which clearly exceeds the 120lm/W of the present fluorescent lamp.

In place of or in addition to a yellow-red AlGaInP LED it is alsopossible to use red AlGaAs LEDs, a combination of several such LEDs withone or more gas-discharge lamps also making good sense. In particular,the use of multiple single light sources of different colors increasesthe control range for the light coloration, that is to say for the colorpoint of the overall lamp system. At the same it must be remembered thatin practice the output of the LEDs can easily be controlled over wideranges, thereby opening up a particularly simple means of controllingthe color point of the lamp system.

The individual light sources may be accommodated in one housing and themixing components designed as described in DE 200 07 134 U1, which tothese ends has been incorporated into this application. For the sake ofcompleteness, however, FIGS. 1 and 2 from this specification and theassociated description will be reproduced here making the necessaryamendments.

FIG. 1 shows a sectional view through a through a lamp system 1according to the invention, comprising a housing 2 having a top wall 3,two side walls 4 and a bottom wall 5 together with two side walls whichare not visible. The side walls are attached at a sloping angle to thetop wall 3, and the bottom wall 5 has a central light outlet aperture 7,which is closed off by a diffuser plate 8. Inside the housing 2 is anelongate fluorescent lamp 6 accommodated on a mount 11, the light fromwhich lamp is prevented from exiting directly through the aperture 7 bya reflector 9 of V-shaped cross-section. The fluorescent lamp 6 emits inthe green-blue and thereby provides the green-blue light fractions ofthe lamp system 1. The green-blue light of the fluorescent lamp 6 isdeflected via the walls of the housing 2 to the aperture 7.

In addition, as the plan view from below in FIG. 2 shows, LEDs 10 aremounted on the bottom wall 5, three on either side of the fluorescentlamp 6. Depending on the particular embodiment, the LEDs emit in theyellow-red or in the red and thereby provide the yellow-red or red lightfractions of the lamp system 1. By adjusting the intensities of the LEDsit is then possible to control the color point and color temperature ofthe lamp system 1. In addition, for further control of the color pointand the color temperature of the lamp system 1 over a wider range, yetfurther LEDs may be fitted, which emit in the green and/or in the blue.The fluorescent lamp 6 may also be provided with an intensity control.

With this mixing component setup, the color mixing of the individuallight sources is particularly effective, since the directly emittedlight is subject to multiple deflections on the walls acting asreflectors, before emerging through the diffuser plate 8. Onedisadvantage, however, is that losses occur with each reflection. Thescope of the invention therefore also extends to other types of mixingarrangements, which use diffusion disks, mirrors and/or integrator rods,for example.

In a further example of an embodiment a whole string of LEDs(represented by dashed lines), which all emit in the yellow-red or red,are used in stead of three LEDs. For extended control of the colorpoint, however, the strings may also contain individual LEDs withemission in the green and/or blue, it being possible to activate thecolors separately from one another.

1. A lamp system having a gas-discharge lamp with a color point in thegreen-blue, an LED with a color point in the yellow-red, and an opticalcomponent for additive mixing of the light from the gas-discharge lampand the LED.
 2. A lamp system as claimed in claim 1, characterized inthat the gas-discharge lamp is a fluorescent lamp.
 3. A lamp system asclaimed in claim 2, characterized in that the fluorescent lamp is alow-pressure mercury-vapor lamp, on which in particular the phosphor BAMis applied for the generation of blue light and/or the phosphor CAT isapplied for the generation of green light.
 4. A lamp system as claimedin claim 1, characterized in that the LED is an inorganic LED, inparticular a red-yellow-emitting AlGaInP LED or a red-emitting AlGaAsLED.
 5. A lamp system as claimed in claim 1, characterized in that thelamp system is provided with a control component for controlling thecolor point of the lamp system.
 6. A lamp system as claimed in claim 5,characterized in that the control component is designed to control thecolor point of the lamp system by controlling the power of thegas-discharge lamp and/or the LED.
 7. A lamp system as claimed in claim5, characterized in that the control component is designed to controlthe color point of the lamp system by controlling the mixingcharacteristics of the optical component.
 8. A method of illuminationcomprising the following stages: generation of light with a color pointin the green-blue by means of a gas-discharge lamp, generation of lightwith a color point in the yellow-red by means of an LED, and additivemixing of the light from the gas-discharge lamp and the LED by means ofan optical component.